Jones (Alligator): Successfully complete Chapter 5: Full House, then get a crowbar, and go to the entrance of the level. Do not go in the car; instead, walk around the house until you find a manhole located at the southeast corner of the level. Enter the manhole to find the mask next to a corpse in the sewers.

Dennis (Wolf): Successfully complete Chapter 5: Full House with a high score.

George (Giraffe): Successfully complete Chapter 6: Clean Hit with a high score.

Brandon (Panther): Successfully complete Chapter 17: Fun & Games with a high score.

Phil (Fish): In Chapter 19: Resolution, talk to the janitors, then search for a box in the sewers.

Louie (Chameleon): Successfully complete the game with the normal ending.

Nigel (Bat): Successfully complete the game with the alternate ending.

Easy "Sewer Alligator" achievement

Successfully complete Chapter 5: Full House, then get a crowbar, and go to the entrance of the level. Do not go in the car; instead, walk around the house until you find a manhole located at the southeast corner of the level. Enter the manhole to find the Jones (Alligator) mask next to a corpse in the sewers and get the "Sewer Alligator" achievement.

Steam achievements

Successfully complete the indicated task to unlock the corresponding achievement. To view your achievements and stats in Steam, select "Community", "My profile", "View all my games", then the game and view stats.

1989: Kill 1989 enemies.

60 To Car: Go to the car 60 times.

Aced It: Get an A+ on any chapter.

Achievement Whore: Unlock all achievements.

Always On Top: Perform every ground kill in the game.

Batman: Clear chapter ?? using only a bat and the bat mask.

Cat Fight: Kill the panthers using the panther mask.

Combo Beginner: Perform a 4x combo.

Combo Intermediate: Perform a 6x combo.

Combo King: Perform a 12x combo.

Combo Master: Perform a 10x combo.

Combo Pro: Perform a 8x combo.

Dog Lover: Kill 99 dogs.

Domino Effect: Throw a weapon at an enemy so that his weapon hits another.

Eye For Details: Collect all the puzzle pieces.

Get A Life: Get A+ on all the chapters.

Guns For Show: Kill at least one enemy with each gun.

I Got New Friends: Unlock all weapons.

Karma: Die 1000 times.

Knife For Pros: Kill at least one enemy with each melee weapon.

Let In Some Air: Destroy 500 glass panels.

Nigel Lowrie: Use a human shield.

Pitcher: Hit at least one enemy with each throwing weapon.

Plain Luck: Kill three or more enemies with the same brick in one throw.

Playing Pool: Kill an enemy with a brick bounced against a wall.

Sewer Alligator: Find the crocodile mask.

Smell Something Burning: Kill the crapping gangster with a fireaxe.

Sounds of Animals Fighting: Wear all masks at least once.

That's It?: Beat the epilogue.

The Boss: Solve the puzzle.

The End?: Beat the mainstory.

These Are My Guns: Complete chapter five barehanded.

This Is It: Beat the epilogue with secret ending.

Two Birds With One Stone: Kill two enemies with the same brick in one throw.